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    Calculates locally in your browser · NEC 220.82 optional method
    Electrical / service sizing

    Optional Method service load

    The optional method exists because the standard method double-counts: it charges the lighting, the receptacles, the appliances and the HVAC separately and adds them, when a house never draws all of it at once. §220.82 takes 100% of the first 10 kVA of the general load and 40% of the rest, then adds the heating or cooling at its own percentage. The result is frequently a smaller service — and occasionally larger, which is why both have to be computed.

    SmallerOptionalHVAC10,800 VAService150 A
    Optional Method
    150 A
    133 A calculated
    Standard Method
    200 A
    184 A calculated
    Difference
    -50 A
    the optional method is smaller
    General load
    21,200 VA
    from 38,000 VA after 100%/40%
    The optional calculation
    One general load through a single demand factor, then the largest heating or cooling clause.
    150 A
    The optional calculation
    LineVARule
    General load38,000lighting, circuits, appliances
    After 100%/40%21,200§220.82(B)
    Heating and cooling10,800Resistance heat at 100% of 10 kW and 40% above — §220.82(C)(4)
    Total32,000general demand plus HVAC
    Service current133.3 Atotal ÷ 240 V
    Optional Method rating150 Anext standard size
    Standard Method rating200 AArticle 220 Part III
    Difference-50 Aoptional is smaller

    The general load of 38,000 VA becomes 21,200 VA after the 100%/40% factor, and resistance heat at 100% of 10 kw and 40% above — §220.82(c)(4) adds 10,800 VA.

    Inspect the model
    Choose a quick result view, a scaled comparison, or the complete diagnostic set.
    Both methods against floor area
    The optional method usually wins on a large house with a big connected load, and can lose on a small one with electric heat.
    Both methods against floor area0.00043.0786.15129.22172.29215.371,000 ft²1,000 ft²1,500 ft²1,500 ft²2,000 ft²2,000 ft²3,000 ft²3,000 ft²4,000 ft²4,000 ft²OptionalStandard
    Where the optional load comes from
    The general load dominates; HVAC is added at its own percentage.
    Where the optional load comes from0.0007552.001.510e+42.266e+43.021e+43.776e+4General demandGeneral demandHVACHVACTotalTotalVA
    Canonical equations
    The exact relationships implemented by this engine.

    min(L, 10k) + 0.4 (L − 10k) · §220.82(B).

    100% of nameplate · §220.82(C)(1).

    100% compressor + 65% supplemental · §220.82(C)(2).

    100% to 10 kW, 40% above · §220.82(C)(4).

    engineering methodology

    A clear path from inputs to results.

    The optional method exists because the standard method double-counts: it charges the lighting, the receptacles, the appliances and the HVAC separately and adds them, when a house never draws all of it at once.

    Step-by-step methodWorked exampleAssumptions explained

    How to use

    1. Enter the floor area and the appliance nameplates.
    2. Add the air conditioning, heat pump and resistance heat.
    3. Read the general load and its 100%/40% demand.
    4. Compare the result with the standard method.

    The formula

    L=min⁡(G,10,000)+0.4 (G−10,000)+LHVACL = \min(G, 10{,}000) + 0.4\,(G - 10{,}000) + L_{HVAC}

    Reference: NFPA 70 §220.82, optional feeder and service load calculations.

    Worked example

    A 2,000 ft² house with electric resistance heat

    Inputs
    • 2,000 ft², two small-appliance circuits, laundry.
    • 12 kW range, 5 kW dryer, 4.5 kW water heater, 6 kW other appliances.
    • 6 kW air conditioning, 12 kW resistance heat.
    Calculation path
    1. 1

      The general load is 6,000 + 3,000 + 1,500 + 12,000 + 5,000 + 4,500 + 6,000 = 38,000 VA.

    2. 2

      Under §220.82(B) that becomes 10,000 + 0.4 × 28,000 = 21,200 VA.

    3. 3

      Resistance heat at 12 kW takes 100% of the first 10 kW and 40% of the rest, or 10,800 VA — larger than the air conditioning at 6,000 VA.

    4. 4

      The total is 32,000 VA, which is 133 A at 240 V.

    5. 5

      The standard method on the same house gives 183.5 A, so the optional method saves a service size.

    Result

    32,000 VA · 133 A · 150 A service.

    Interpreting the result

    The two methods can disagree in either direction. On a large house with a big connected load the optional method almost always wins; on a small house with electric resistance heat the HVAC clause can make it larger than the standard method, which is why the code allows either rather than requiring one.

    Assumptions & limitations

    • A one-family dwelling with a service of 100 A or more.
    • General lighting at 3 VA/ft².
    • The §220.82(C) clauses are alternatives, not additive.
    • No largest-motor adder or EV charging.

    Frequently asked questions

    Which method should I use?

    Either — the code permits both. Compute both and use the smaller, but the optional method is only available for a dwelling with a 100 A or more service.

    What counts as the general load?

    Lighting, the small-appliance and laundry circuits, and the nameplate rating of every appliance fastened in place — range, dryer, water heater, disposer, dishwasher and so on.

    Can I use it for a multifamily building?

    §220.84 covers multifamily dwellings with a different set of factors. The single-dwelling optional method does not apply.

    Why is the HVAC clause not additive?

    Because heating and cooling never run together. The code takes the largest single clause, which for a heat pump is the compressor at 100% plus 65% of the supplemental resistance.

    Does the 100 A floor ever bind?

    On a small house with gas heat and no large appliances, yes. The calculation can come out below 100 A and the service still has to be 100 A.

    Methodology last reviewed 2026-10-22. Results are informational and not financial or engineering advice — see our disclaimer.